Method and device for carrier activation in carrier aggregation system

ABSTRACT

The present invention relates to a method and a device for cell activation in a carrier aggregation system, and the method for activating a cell of a terminal according to one embodiment of the present invention comprises: a step for receiving an activation message of a first cell; a step for activating the first cell when the message of the first cell is received; an information obtaining step for obtaining uplink activation information of the first cell; and a transmission determination step for determining whether to execute an uplink transmission according to the uplink activation information. According to an embodiment of the present invention, efficient carrier management plan can be provided.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of prior application Ser.No. 14/009,963, filed on Oct. 4, 2013, which is a U.S. National Stageapplication under 35 U.S.C. § 371 of an International application numberPCT/KR2012/002592, filed on Apr. 5, 2012, which is based on and claimedpriority under 35 U.S.C. § 119(e) of a U.S. Provisional application Ser.No. 61/471,872, filed on Apr. 5, 2011, in the U.S. Patent and TrademarkOffice and of a U.S. Provisional application Ser. No. 61/484,645, filedon May 10, 2011, in the U.S. Patent and Trademark Office, and under 35U.S.C § 119(a) of a Korean patent application number 10-2012-0035573,filed on Apr. 5, 2012, in the Korean Intellectual Property Office, thedisclosure of each of which is incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The present invention relates to a carrier activation method andapparatus for use in a carrier aggregation system.

BACKGROUND ART

The mobile communication system has been developed for the user tocommunicate on the move. With the rapid advance of technologies, themobile communication system has evolved to the level capable ofproviding high speed data communication service as well as voicetelephony service. Recently, as one of the next generation mobilecommunication system, Long Term Evolution (LTE) is on thestandardization by the 3rd Generation Partnership Project (3GPP). LTE isa technology designed to provide high speed packet-based communicationof up to 100 Mbps and aims at commercial deployment around 2010timeframe.

Meanwhile, unlike voice service, the data service is provided on theresource determined according to the data amount to be transmitted andchannel condition. Accordingly, the wireless communication system,especially cellular communication, is provided with a scheduler managestransmission resource allocation in consideration of the requiredresource amount, channel condition, data amount, etc. This is the factin the LTE system as the next generation mobile communication system,and the scheduler located at the base station manages the transmissionresource allocation.

Recent studies are focused on the LTE-Advanced (LTE-A) for improvingdata rate with the adaptation of several new techniques to legacy LTEsystem. Carrier Aggregation (CA) is one of such technologies. CA is thetechnology that aggregates a plurality of carriers for uplink anddownlink transmission between a User Equipment (UE) and an evolved NodeB (eNB) so as to increases the data reception amount/reception data rateor transmission amount/transmission data rate in proportion to thenumber of aggregated carriers. In LTE, the cell operating on the maincarrier frequency is referred to as Primary Cell (PCell) and the othercells operating on other frequency carriers are referred to as SecondaryCell (SCell).

Meanwhile, with the introduction of repeater and Remote Radio Head(RRH), the positions of antennas responsible for the radiotransmission/reception change (e.g. the transmit/receive antennas forthe secondary carrier may be located at the RRHs while thetransmit/receive antennas for the primary carrier are located at theeNB) and, in this case, it is prefer to acquire the uplink transmissiontiming to a receive antenna near the terminal location rather than theuplink transmission timing to a receive antenna far from the terminallocation. This means that a plurality of uplink transmission timings mayexist and thus there is a need of a method for managing carriersefficiently in a carrier aggregation scenario including a plurality ofuplink transmission timings.

DISCLOSURE OF INVENTION Technical Problem

The present disclosure is proposed to solve the above problem and aimsto provide an efficient carrier management method.

Solution to Problem

In accordance with an aspect of the present disclosure, a cellactivation method of a terminal includes receiving a first cellactivation message, activating, when the first cell activation messageis received, the first cell, acquiring uplink activation information onthe first cell, and determining whether to perform uplink transmissiondepending on the uplink activation information.

In accordance with another aspect of the present disclosure, a terminalincludes a transceiver which receives an activation message for a firstcell, a scheduler which activates, when the activation message for thefirst cell is received, the first cell, acquires uplink activationinformation on the first cell, and determines whether to perform uplinktransmission according to the uplink activation information.

In accordance with another aspect of the present disclosure, a cellactivation method of a base station includes transmitting an activationmessage for a first cell to a terminal, determining whether uplinktransmission timing synchronization for the first cell is required, andtransmitting, when uplink transmission timing synchronization for thefirst cell is required, an indicator indicating suspension of uplinktransmission in the first cell to the terminal.

In accordance with still another aspect of the present disclosure, abase station includes a transceiver which transmits an activationmessage for a first cell to a terminal and a scheduler which determineswhether uplink transmission timing synchronization for the first cell isrequired and controls, when uplink transmission timing synchronizationfor the first cell is required, the transceiver to transmit an indicatorindicating suspension of uplink transmission in the first cell to theterminal.

Advantageous Effects of Invention

The present disclosure is capable of providing an efficient carriermanagement method.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating network architecture of a 3GPP LTEsystem according to an embodiment of the present disclosure.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

FIG. 3 is a diagram illustrating an exemplary situation of carrieraggregation in the LTE system to which the present invention is applied.

FIGS. 4A and 4B are diagrams illustrating a principle of uplink timingsynchronization in the OFDM-based 3GPP LTE system to which the presentinvention is applied.

FIG. 5 is a diagram illustrating an exemplary scenario requiring aplurality of uplink timings in carrier aggregation.

FIG. 6 is a signal flow diagram illustrating a cell activation procedureaccording to an embodiment of the present disclosure.

FIG. 7 is a flowchart illustrating a cell activation procedure of the UE601 according to an embodiment of FIG. 6.

FIG. 8 is a signaling diagram illustrating a cell activation procedureaccording to another embodiment of the present disclosure.

FIG. 9 is a flowchart illustrating the cell activation procedure of theeNB 811 according to the embodiment of FIG. 8.

FIG. 10 is a flowchart illustrating the cell activation procedure of theUE 801 according to the embodiment of FIG. 8.

FIG. 11 is a block diagram illustrating the eNB according to anembodiment of the present disclosure.

FIG. 12 is a block diagram illustrating the UE according to anembodiment of the present disclosure.

MODE FOR THE INVENTION

Exemplary embodiments of the present invention are described withreference to the accompanying drawings in detail.

Detailed description of well-known functions and structures incorporatedherein may be omitted to avoid obscuring the subject matter of thepresent invention. This aims to omit unnecessary description so as tomake the subject matter of the present invention clear.

For the same reason, some of elements are exaggerated, omitted orsimplified in the drawings and the elements may have sizes and/or shapesdifferent from those shown in drawings, in practice. The same referencenumbers are used throughout the drawings to refer to the same or likeparts.

Hereinafter, exemplary embodiments of the present invention aredescribed with reference to the accompanying drawings in detail.

The present disclosure proposes a method for activating a serving cell(e.g. SCell) operating on a secondary carrier configured for use in thecarrier aggregations with a plurality of uplink timings. According tothe legacy carrier aggregation operation, the mobile communicationsystem configures serving cells on the secondary carriers and activatesthe serving cell to transmit and receive data through the serving cells.According to an embodiment of the present disclosure, the terminaloperates differently depending when it maintains valid uplinktransmission timing synchronization for the activated serving cells.

If the terminal has acquired or is maintaining the uplink transmissiontiming synchronization with the serving cell commanded/indicated to beactivated (i.e. uplink transmission timing synchronization for theserving cell or uplink transmission timing synchronization for otherserving cell to which the same uplink transmission timing as the servingcell is applied is maintained), the uplink transmission of PhysicalUplink Shared Channel (PUSCH) scheduled for the serving cell or SoundingReference Symbol (SRS) configured for the corresponding serving cell isperformed at the corresponding timing immediately.

Otherwise if the terminal has no uplink transmission timingsynchronization with the serving cell command/indicated to be activated,the scheduled PUSCH uplink transmission is ignored the SRS uplinktransmission is suspended until receiving uplink transmission timinginformation through random access procedure in the corresponding servingcell. In this case, the PUSCH uplink transmission and suspended SRSuplink transmission are started after acquiring uplink transmissiontiming synchronization based on the uplink transmission timinginformation acquired through the random access procedure in thecorresponding serving cell.

There are two methods for the terminal to determine whether the uplinktransmission timing with the serving cell commanded/indicated to beactivated is maintained. In the first method, the terminal determines initself whether it maintains uplink transmission timing synchronizationwith the serving cell or other serving cell using the same uplinktransmission timing as the corresponding serving cell. In the secondmethod, the base station notifies the terminal explicitly throughsignaling whether PUSCH and SRS uplink transmission is possibleimmediately after activation or after acquiring uplink transmissiontiming synchronization upon receipt of the uplink transmission timinginformation through random access procedure in commanding/indicatingactivation of the serving cell.

FIG. 1 is a diagram illustrating network architecture of a 3GPP LTEsystem according to an embodiment of the present disclosure. Accordingto an embodiment of the present disclosure, the LTE network includesevolved Node Bs (eNBs) 105, 110, 115, and 120, a Mobility ManagementEntity (MME) 125, and a Serving-Gateway (S-GW) 130. The User Equipment(hereinafter, referred to as UE) 135 connects to an external network viaeNBs 105, 110, 115, and 120 and the S-GW 130. The User Equipment (UE)135 connects to an external network through the eNB 105 and SGW 130. TheeNBs 105, 110, 115, and 120 correspond to the legacy node B of UMTSsystem. The eNB 105 establishes a radio channel with the UE 135 and isresponsible for complex functions as compared to the legacy node B. Inthe LTE system, all the user traffic including real time services suchas Voice over Internet Protocol (VoIP) are provided through a sharedchannel and thus there is a need of a device which is located in the eNBto schedule data based on the state information such as UE bufferconditions, power headroom state, and channel state. Typically, one eNBcontrols a plurality of cells. In order to secure the data rate of up to100 Mbps, the LTE system adopts Orthogonal Frequency DivisionMultiplexing (OFDM) as a radio access technology. Also, the LTE systemadopts Adaptive Modulation and Coding (AMC) to determine the modulationscheme and channel coding rate in adaptation to the channel condition ofthe UE. The S-GW 130 is an entity to provide data bearers so as toestablish and release data bearers under the control of the MME 125. MME125 is responsible for various control functions and connected to aplurality of eNBs 105, 110, 115, and 120.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied. Referring to FIG. 2, theprotocol stack of the LTE system includes Packet Data ConvergenceProtocol (PDCP) 205 and 240, Radio Link Control (RLC) 210 and 235,Medium Access Control (MAC) 215 and 230, and Physical (PHY) 220 and 225.The PDCP is responsible for IP header compression/decompression,ciphering, and Integrity Protection. The RRC 208 and 238 defines thehigher layer control information message transmission and relatedoperation/procedure for handling radio resource. The RLC 210 and 235 isresponsible for segmenting the PDCP Protocol Data Unit (PDU) intoappropriate size. The MAC 215 and 230 is responsible for establishingconnection to a plurality of RLC entities so as to multiplex the RLCPDUs into MAC PDUs and demultiplex the MAC PDUs into RLC PDUs. The PHY220 and 225 performs channel coding on the MAC PDU and modulates the MACPDU into OFDM symbols to transmit over radio channel or performsdemodulating and channel-decoding on the received OFDM symbols anddelivers the decoded data to the higher layer.

FIG. 3 is a diagram illustrating an exemplary situation of carrieraggregation in the LTE system to which the present invention is applied.Referring to FIG. 3, typically an eNB can use multiple carrierstransmitted and receive in different frequency bands. For example, theeNB 305 can be configured to use the carrier 315 with center frequencyf1 and the carrier 310 with center frequency f3. If carrier aggregationis not supported, the UE 330 has to transmit/receive data unit one ofthe carriers 310 and 315. However, the UE 330 having the carrieraggregation capability can transmit/receive data using both the carriers310 and 315. The eNB may increase the amount of the resource to beallocated to the UE having the carrier aggregation capability inadaptation to the channel condition of the UE so as to improve the datarate of the UE.

Although the above description has been directed to the transmitter sideof the eNB, it is applicable to the receiver side of the eNB in the samemanner Unlike the legacy UE transmitting data using one of the pluralitycarriers, the carrier aggregation-enabled terminal is capable oftransmitting data using plural carriers simultaneously so as to increasethe data rate. In case that a cell is configured with one downlinkcarrier and one uplink carrier as a conventional concept, the carrieraggregation can be understood as if the UE communicates data viamultiple cells. With the use of carrier aggregation, the peak data rateincreases in proportion to the number of aggregated carriers. In thefollowing description, the phrase “the UE receives data through acertain downlink carrier or transmits data through a certain uplinkcarrier” means to transmit or receive data through control and datachannels provided in a cell corresponding to center frequencies andfrequency bands of the downlink and uplink carriers. Although thedescription is directed to an LTE mobile communication system forexplanation convenience, the present invention can be applied to othertypes of wireless communication systems supporting carrier aggregation.

FIGS. 4A and 4B are diagrams illustrating a principle of uplink timingsynchronization in the OFDM-based 3GPP LTE system to which the presentinvention is applied. The UE1 is located near the eNB and the UE2 islocated far from the eNB. T_pro1 indicates the first propagation delaytime to the UE1, and T_pro2 indicates the second propagation delay tothe UE2. The UE1 locates near the eNB as compared to the UE2 and thushas a relatively short propagation delay. In FIG. 4A, T_pro1 is 0.333us, and T_pro2 is 3.33 us.

Referring to FIG. 4B, the initial uplink timing of the UE 1 491 and UE 2492 within a cell of the eNB 490 mismatches the uplink timings of theUEs with the cell found by the eNB 490. Reference number 401 denotesuplink OFDM symbol transmission timing of the UE1 491, and referencenumber 403 denotes uplink OFDM symbol transmission timing of the UE2492. By taking notice of the uplink transmission propagation delays ofthe UE1 491 and UE2 492, the eNB 490 may receive the uplink OFDM symbolsat the timings as denoted by reference numbers 407 (for UE1) and 409(for UE 2). The UE1's uplink symbol is received by the eNB 490 at thetiming 407 with a short propagation delay while the UE2's uplink symboltransmitted is received by the eNB 490 at the timing 409 with relativelylong propagation delay. The eNB 490 has a reference reception timing405.

Since the timings 407 and 409 precede the synchronization between theuplink transmission timings of the UE1 and UE2, the uplink OFDM symbolreception and decoding start timing 405 of the eNB, the UE1's uplinkOFDM symbol reception timing 407, and the UE2's uplink OFDM symbolreception timing 409 are different among each other. In this case, theuplink symbols transmitted by the UE1 and UE2 are not orthogonal so asto interfere to each other and, as a consequence, the eNB is likely tofail decoding the uplink symbols transmitted, at the timing 401 and 403,by the UE1 and UE2 due to the interference and the mismatch between theuplink symbol reception timings 407 and 409.

Uplink timing synchronization is a procedure for acquiring the eNB'suplink symbol reception timings with the UE1 491 and UE2 492 and, if theuplink timing synchronization procedure completes, it is possible toacquire the synchronization among the eNB's uplink OFDM symbol receptionand decoding start timing, UE1's uplink OFDM symbol reception timing,and UE2's uplink OFDM symbol reception timing as denoted by referencenumbers 411, 413, and 415. In the uplink timing synchronizationprocedure, the eNB 490 transmits Timing Advance (hereinafter, referredto as TA) information to the UEs to notify of the timing adjustmentamount. The eNB can transmit the TA information in the Timing AdvanceCommence MAC Control Element (TAC MAC CE) or in the Random AccessResponse (RAR) message in response to the random access preambletransmitted by the UE for initial access.

FIG. 5 is a diagram illustrating an exemplary scenario requiring aplurality of uplink timings in carrier aggregation. The Remote RadioHeads (RRHs) 503 operating on frequency band F2 507 are deployed aroundthe macro eNB 501 using frequency band F1 505. If the UE uses both themacro eNB 501 and RRH 503 (i.e. if the UE near the RRH 503 aggregates F1frequency band and F2 frequency band for uplink transmission), thedownlink/uplink transmission between the UE and the RRH 503 has shortpropagation delay and the downlink/uplink transmission between the UEand the macro eNB 501 has relatively long propagation delay. This meansthat the uplink transmission timing to the RRH 503 differs from theuplink transmission timing to the macro eNB 501. There is a need of aplurality of uplink transmission timings in the above carrieraggregation scenario and, in order to acquire initial uplinktransmission timing, it is necessary to configure an uplink transmissiontiming through random access procedure on F2 for the RRH 503 and anotheruplink transmission timing through random access procedure on F1 for themacro eNB 501. This means that if multiple uplink transmission timingsexist in the carrier aggregation it is necessary to perform the randomaccess procedure in multiple cells for synchronizing the uplinktransmission timing. It is not necessary to perform the random accessprocedures at the same timings in the plural cells.

In the present disclosure, the carriers having the same uplink timingsare sorted into a Timing Advance Group (TAG). For example, if one PCelland three SCells A, B, and C are aggregated, the PCell and SCell A havethe same uplink timing, and the SCell B and SCell C have the same uplinktiming, the PCell and SCell A may be grouped into TAG #0 and the SCell Band SCell C into TAB #1. The TAG #0 including the PCell is referred toas Primary TAG (PTAG) and the TAG #1 including no PCell is referred toas STAG. PCell is the serving cell operating on the primary carrier towhich RRC Connection Establishment has been performed initially or theHandover (HO) target cell.

FIG. 6 is a signal flow diagram illustrating a cell activation procedureaccording to an embodiment of the present disclosure. The base station611 determines to configure the serving cells (SCell #1 615 and SCell #2617) on the secondary carriers to be aggregated to the UE 601 capable ofcarrier aggregation in the serving cell of the primary carrier (PCell)613 and configures the SCell #1 615 and SCell #2 617 as the carrieraggregation component cells of the UE 601 by transmitting configurationinformation on the SCell #1 625 and SCell #2 617 through a RRC layermessage at operation 621. The RRC layer message may beRRCConnectionReconfiguration message defined in the 3GPP TS36.331 RRC.The configuration information on the SCell #1 615 and SCell #2 617 mayinclude the channel configuration information on the serving cells 615and 617 and the uplink Timing Advance Group (TAG) identifier. Thechannel configuration information on the serving cells 615 and 617 mayinclude the configuration information on the Sounding Reference Symbol(SRS) channel and the configuration information on the random accesschannel. The SRS channel is a physical (PHY) channel carrying the signalfor use in uplink channel estimation of the eNB.

In the embodiment of FIG. 6, it is assumed that the TAG identifier ofthe SCell #1 615 is identical with the TAG identifier of the PCell 613on the current primary carrier and the TAG identifier of the SCell #2617 differs from the TAG identifier of the PCell 613 and SCell #1 615.That is, the uplink transmission timings of the PCell 613 and the SCell#1 615 are identical with each other while the uplink transmissiontiming of the SCell #2 617 differs from the uplink transmission timingof the PCell 613 and SCell #1 615. The random access channelconfiguration information may include the information on both the SCell#1 615 and SCell #2 617 or the information on only the SCell #2 617having the new uplink transmission timing. In the embodiment of FIG. 6,it is assumed that the information on only the SCell #2 617 having thenew uplink transmission timing. The terminal 601 which has received themessage of operation 621 stores/configures the configuration informationon the SCell #1 615 and SCell #2 617 having the new uplink transmissiontiming at operation 625.

If eNB 611 has determined to activate the SCell #1 615 configured forthe UE 601, the UE 601 activates the SCell #1 615 by transmitting a MAClayer message at operation 631. The MAC layer message may be ActivationMAC Control Element (CE) message defined in the 3GPP TS36.321 MAC. TheActivation MAC CE include an indicator indicating activation of SCell #1615.

Upon receipt of the message of operation 631, the UE activates the SCell#1 615, transmits SRS using the timing resource allocated with the SRSchannel configuration information received at operation 621, andperforms, if the scheduling information on uplink transmission for theSCell #1 615 is received, uplink transmission using the timing andresource allocated based on the scheduling information at operation 633.

The terminal 601 transmits SRS through SCell #1 615 at operation 635.The UE 601 receives the scheduling information for uplink transmissionin SCell #1 615 through Physical Downlink Control Channel (PDCCH) atoperation 637. The UE 601 performs uplink transmission in the SCell #1615 based on the scheduling information of the operation 637 atoperation 639. If the eNB 611 determines to activate the SCell #2 617configured for the UE 601, it transmits a MAC layer message to activatethe SCell #2 617 at operation 641. The MAC layer message may beActivation MAC Control Element (CE) message defined in the 3GPP TS36.321 MAC. The Activation MAC CE includes an indicator for activatingthe SCell #2 617.

The UE 601 received the message of operation 641 activates the SCell #2617 or suspends SRS transmission indicated in the SRS channelconfiguration information received at operation 621 and ignores, if thescheduling information for uplink transmission in the SCell #2 617, thescheduling information at operation 643. The SRS transmission in theSCell #2 617 is suspended at operation 645. That is, the UE does nottransmit SRS in the SCell #2 617. The UE 601 receives the uplinktransmission scheduling information for the SCell #2 through PDCCH atoperation 647.

If the uplink transmission scheduling information for the SCell #2 617is received, the UE 601 ignores the scheduling information at operation649. That is, in the state that the SCell #2 617 is activated, it ispossible to receive downlink channel but not to transmit uplink channel.However, if a random access initiation command is received, it ispossible to transmit a Random Access Preamble in uplink.

The eNB 611 which has determined to synchronize the uplink transmissiontimings of the UE 601 in the SCell #2 through random access procedurecommands the UE 601 to perform random access in the SCell #2 617 atoperation 651. The random access command message may be a physicalcontrol message called PDCCH order defined in the 3GPP TS36.212 E-UTRAmultiplexing and channel coding. If it is commanded to perform randomaccess in the SCell #2 617, the UE 601 transmits a Random AccessPreamble in the SCell #2 617 at operation 653.

If a response message is received in response to the Random AccessPreamble at operation 655, the UE 601 synchronizes the uplinktransmission timing in the SCell #2 617 using the uplink timinginformation (Timing Advance, TA) included in the Random Access Responsemessage. By matching the reception timing of the message of operation655 to the uplink transmission timing to the SCell #2, it the actualuplink transmission timing may mismatch but the uplink transmission maybe possible after a predetermined time since the receipt of the messageof 655.

If the uplink transmission synchronization is acquired in the SCell #2617, the SRS transmission based on the SRS channel configurationinformation 621 starts and, if the scheduling information for uplinktransmission in the SCell #2 is received, the UE 601 performs uplinktransmission at the timing on the resource indicated in the schedulinginformation at operation 661. The UE 601 transmits SRS in the SCell #2617 at operation 663. The UE 601 receives the scheduling information foruplink transmission in the SCell #2 617 through PDCCH at operation 665.The UE 601 performs uplink transmission in the SCell #2 based on thescheduling information of operation 665.

That is, if a message for activating the SCell configured for carrieraggregation is received, the UE 601 and if the UE 601 maintains (valid)uplink transmission timing for the activated (if the uplink transmissiontiming for the SCell is maintained or the uplink transmission timing foranother cell using the same uplink timing as the SCell is maintained),the UE 601 starts SRS transmission using the timing and resourceallocated based on the SRS channel configuration information afteractivation of the SCell and, if the scheduling information for uplinktransmission in the SCell is received, performs uplink schedulingaccording to the received scheduling information. If the UE receives themessage for activating the SCell configured for carrier aggregation andif the (valid) uplink transmission timing for the activated SCell ismaintained, the UE 601 suspends the SRS transmission based on the SRSchannel configuration information and ignores the scheduling informationreceived for uplink transmission in the SCell. The SCell has beenactivated by the activation message but no uplink transmission occurs.That is, in the case that the UE commands to perform random access, theUE may transmit a Random Access Preamble, the suspension of the SRStransmission and the ignorance of scheduling information for uplinktransmission are released when the UE performs random access procedurein the corresponding cell to receive the uplink timing informationthrough the Random Access Response message and synchronize the uplinktransmission timing and, since then, the SRS transmission starts basedon the SRS channel configuration information and the uplink and uplinktransmission is performed based on the uplink scheduling information.

FIG. 7 is a flowchart illustrating a cell activation procedure of the UE601 according to an embodiment of FIG. 6. If an activation requestmessage for the SCell configured for carrier aggregation is received atoperation 701, the UE determines whether the uplink transmission timingis maintained at operation 711. If the uplink transmission timing in theSCell or in another serving cell using the same uplink transmissiontiming as the SCell is maintained, the UE activates the SCell, startstransmitting SRS according to the SRS channel configuration, andperforms uplink transmission in the SCell according to the uplinkscheduling information at operation 721. If no uplink transmissiontiming for the SCell or the serving cell using the same uplinktransmission timing as the SCell is acquired (synchronized), the UEactivates the SCell, suspends SRS transmission according to the SRSchannel configuration, and ignores the uplink scheduling information onthe SCell, resulting in not uplink transmission, at operation 731.However, if the eNB 611 commands the UE 601 to perform in the SCell, theUE 601 may transmit the Random Access Preamble in the SCell. If theTiming Advance (TA) information on the SCell is acquired through therandom access procedure in the SCell and the uplink transmission timingis acquired at operation 741, the UE starts transmitting SRS suspendedin the SCell and performs uplink transmission according to the uplinkscheduling information on the SCell at operation 751.

FIG. 8 is a signaling diagram illustrating a cell activation procedureaccording to another embodiment of the present disclosure. The eNB 811determines to configure the serving cells (SCell #1 815 and SCell #2817) operating on the secondary carriers to be aggregated for the UE 801capable of carrier aggregation in the serving cell (PCell) 813 operatingon the primary carrier and transmits the configuration information onthe SCell #1 815 and SCell #2 817 through an RRC layer message toconfigure the SCell #1 815 and SCell #2 817 as the carrieraggregation-configured cells of the UE 801 at operation 821. The RRClayer message may be the RRCConnectionReconfiguration message defined inthe 3GPP TS36 Radio Resource Control (RRC). The configurationinformation on the SCell #1 815 and SCell #2 817 may include the channelconfiguration information and the Timing Advance Group (TAG) identifierof the serving cells 815 and 817. The channel configuration informationof the serving cell may include Sounding Reference Symbol (SRS) channelconfiguration information and random access channel configurationinformation. The SRS channel is the physical (PHY) channel carrying thesignal for used in uplink channel estimation of the eNB.

In the embodiment of FIG. 8, it is assumed that the TAG identifier ofthe SCell #1 815 is identical with the TAG identifier of the PCell 815on the current primary carrier and the TAG identifier of the SCell #2817 is different from the TAG identifier of the PCell 813 and SCell #1815. That is, the uplink transmission timings of the PCell 813 and theSCell #2 817 are identical with each other, and the uplink transmissiontiming of the SCell #2 817 and the uplink transmission timings of thePCell 813 and the SCell #1 815 are different from each other. The randomaccess channel configuration information may include the information onboth the SCell #1 815 and SCell #817 or only the SCell #2 817 having thenew uplink transmission timing. In the embodiment of FIG. 8, it isassumed that the information on the SCell #2 817 having the new uplinktransmission timing is included. Upon receipt of the message ofoperation 821, the UE 801 stores/configures the configurationinformation on the SCell #1 815 and SCell #2 817 for carrier aggregationat operation 825.

If it is determined to activate the SCell #1 815 configured to the UE,the eNB 811 transmits a MAC layer message to activate the SCell #1 815at operation 831. The MAC layer message may be the Activation MAC CEmessage defined in the 3GPP TS36.321 MAC. The Activation MAC CE includesthe indicator for activating the SCell #1 815 and the uplink suspensionindicator information. It is assumed that the signaling of operation 831has the uplink suspension indicator information is set to FALSE. If theuplink suspension indicator information is set to FALSE, this allows theUE 801 to perform uplink transmission in the SCell after its activation.

If the message of operation 831 is received, the UE 801 activates theSCell #1 815, transmits SRS using the resource of the timing allocatedwith the SRS channel configuration information received at operation 821and, if the scheduling information on the uplink transmission for theSCell #1 815, performs uplink transmission using the timing and resourceallocated with the scheduling information at operation 833.

The UE 801 performs SRS transmission in the SCell #1 815 at operation835. The UE 801 receives the scheduling information for uplinktransmission in the SCell #1 815 through the Physical Downlink ControlChannel (PDCCH) at operation 837. The UE 801 performs uplinktransmission in the SCell #815 based on the scheduling information ofoperation 837 at operation 839.

If it is determined to activate the SCell #2 817 configured to the UE801, the eNB 811 transmits a MAC layer message to activate the SCell #2817 at operation 841. The MAC layer message may be the Activation MACControl Element (CE) message defined in the 3GPP TS36.321. TheActivation MAC CE includes the indicator for activating the SCell #2 anduplink suspension indicator information. It is assumed that the signalof operation 841 includes the uplink suspension indicator informationset to TRUE. If the uplink suspension indicator information is set toTRUE, this indicates that the UE 801 suspends uplink transmission in theSCell until the uplink transmission timing is synchronized with theacquisition of uplink timing information (TA) on the SCell throughrandom access procedure. For example, the configured SRS channeltransmission is suspended and, if the scheduling information on theuplink transmission in the SCell is received through PDCCH, ignores thescheduling information on the uplink transmission, resulting in nouplink transmission. In the eNB commands to perform the random access inthe SCell, however, it is possible to transmit the Random AccessPreamble in uplink. If the uplink suspension indicator information isset to TRUE, the UE 801 has to perform the operation associated to theTRUE information value regardless of whether the uplink transmissiontiming on the cell is maintained or not.

If the message of operation 841 is received, the UE 801 activates theSCell #2 or suspends the SRS transmission based on the SRS channelconfiguration information received at operation 821 and ignores, if anyscheduling information on uplink transmission in the SCell #2 817, thescheduling information at operation 843. The UE 801 suspends the SRStransmission in the SCell #2 817 at operation 845. That is, the UE 801does not transmit SRS in the SCell #2 817. The UE 801 receives thescheduling information for uplink transmission in the SCell #2 817through PDCCH. If the scheduling information for uplink transmission inthe SCell #2 817 is received, the UE 801 ignores the schedulinginformation at operation 849. That is, although the SCell #2 817 isactivated, the uplink transmission is suspended but the downlink channelreception is permitted (i.e. the uplink transmission is impossible inthe SCell #2 817). In the case that there is random access command ofthe eNB 811, however, the UE 801 is capable of transmitting the RandomAccess Preamble in uplink.

If it is determined to synchronize the uplink transmission timing of theUE 801 through random access procedure in the SCell #2, the eNB 811command the UE 801 to perform the random access in the SCell #2 atoperation 851. The random access command message may be a physicalcontrol message called PDCCH order defined in the 3GPP TS36.212 E-UTRAMultiplexing and channel coding. If the random access execution commandin SCell #2 817 is received, the terminal 801 transmits a Random AccessPreamble through the SCell #2 817 at operation 853. If a Random AccessResponse message is received at operation 855, the UE 801 synchronizesthe uplink transmission timing of the SCell #2 817 using the SCell #2uplink timing information (TA) included in the Random Access Responsemessage. The timing of receiving the message of operation 855 and thetiming capable of actual uplink transmission in match with the uplinktransmission timing in the SCell #2 817 may mismatch each other. The UEmay perform uplink transmission in a certain time after the receipt ofthe message of operation 855.

If the uplink transmission timing in the SCell #2 817 is synchronized,the UE starts SRS transmission based on the SRS channel configurationinformation received at operation 821 and, if the scheduling informationfor uplink transmission in the SCell #2 817 is received, the UE 801performs uplink transmission using the timing and resource allocatedwith the scheduling information at operation 861. The UE 801 performsSRS transmission in the SCell #2 817 at operation 863. The UE 801receives the scheduling information for uplink transmission in the SCell#2 817 through PDCCH at operation 865. The UE 801 performs uplinktransmission in the SCell #2 817 based on the scheduling information ofoperation 865.

The uplink suspension indicator is transmitted in the SCell activationmessage in the above embodiments. However, the uplink suspensionindicator may be transmitted using a separate message for the SCell thathas been already activated at operation 871. The message includes theidentifier information on the corresponding SCell and uplink suspensionindicator information. if the SCell identifier information indicates theSCell #2 817 and the uplink suspension indicator is set to TRUE, the UEsuspends the uplink transmission in the SCell #2 817 until the uplinktransmission timing is synchronized with acquisition of the uplinktiming information for the SCell #2 817 through random access procedureregardless of the uplink transmission timing in the SCell #2 817. Forexample, the configured SRS channel transmission is suspended, and, ifthe scheduling information for uplink transmission in the SCell throughPDCCH, the UE 801 ignores the scheduling information on uplinktransmission, resulting in not uplink transmission, at operation 873. Ifthe eNB commands to perform the random access in the SCell, however, itis possible to transmit a Random Access Preamble in uplink.

That is, the UE 801 performs the SRS transmission configured for theSCell and scheduled uplink transmission or suspends the uplinktransmission with the exception of the Random Access Preambletransmission (if eNB commands Random Access Preamble transmission) untilthe uplink transmission timing is (re)synchronized with the acquisitionof the uplink timing information (TA) for the SCell through the nextrandom access procedure, according to the uplink suspension indicatorvalue received from the eNB 811. For example, the configured SRS channeltransmission is suspended and, if the scheduling information for uplinktransmission in the SCell through PDCCH is received, the UE 801 ignoresthe scheduling information for uplink transmission and skipscorresponding uplink transmission.

FIG. 9 is a flowchart illustrating the cell activation procedure of theeNB 811 according to the embodiment of FIG. 8. The present disclosure isapplied when the eNB 811 communicates with the UE 801 capable of carrieraggregation at operation 901. The eNB 811 checks whether the uplinktransmission timing (re)synchronization is required in the SCell for theUE 801 at operation 911. For example, if it is necessary to activate theSCell requiring uplink transmission timing different from those of otherserving cells activated for the UE 801 or if the SCell has beenactivated already but has a problem in uplink transmission, the eNB 811may determine that there is a need of re(synchronizing) the uplinktransmission timing for the SCell. If it is determined that there is noneed of (re)synchronizing the uplink transmission timing in the SCellfor the UE at operation 911, the eNB 811 configures the correspondingSCell identifier information and sets the uplink suspension indicatorinformation to FALSE at operation 921. Otherwise if it is determinedthat there is a need of (re)synchronizing the uplink transmission timingin the SCell for the UE, the eNB 811 configures the SCell identifierinformation and set the uplink suspension indicator information to TRUEat operation 931. The eNB transmits the SCell identifier information anduplink suspension indicator information in the SCell activation message(e.g. Activation MAC CE) or a new or another legacy message at operation941.

FIG. 10 is a flowchart illustrating the cell activation procedure of theUE 801 according to the embodiment of FIG. 8.

The UE 801 receives an activation message for the SCell configured forcarrier aggregation or a separate message for the SCell which has beenalready activated at operation 1001. The message may be replaced byanother MAC layer or RRC layer message or a new MAC layer or RRC layermessage defined for uplink suspension indicator information. The UE 801checks the uplink suspension indication information value correspondingto the SCell identifier included in the message at operation 1011. Ifthe uplink suspension indicator information value is set to FALSE, theUE 801 starts SRS transmission according to the SRS channelconfiguration for the SCell and performs uplink transmission in theSCell according to the received uplink scheduling information atoperation 1021. Otherwise if the uplink suspension indicator informationvalue is set to TRUE, the UE 801 checks whether the TAT(timeAlignmentTimer) corresponding to the SCell is running currently atoperation 1031. The TAT is the timer for verifying the validity of theuplink transmission timing information (TA) received from the eNB, thetimer (re)starting upon receipt of the TA information from the eNB and,if it expires, the uplink transmission timing being not valid anylonger. If the TAT for the SCell is running, the UE 801 stops the timerat operation 1041, suspends the SRS transmission according to the SRSchannel configuration, and does not perform corresponding uplinktransmission at operation 1051. However, if the eNB commands to performrandom access in the SCell, the Random Access Preamble may betransmitted in the SCell. if the random access is performed in the SCell so are to acquire TA information for the SCell and (re)synchronizethe uplink transmission timing at operation 1061, the UE 801 starts theSRS transmission in the SCell and performs uplink transmission accordingto the uplink scheduling information at operation 1071.

FIG. 11 is a block diagram illustrating the eNB according to anembodiment of the present disclosure. The physical transceiver 1101 isresponsible for communication with a UE. The scheduler 1111 isresponsible for scheduling downlink and uplink transmissions for UEs andcells (PCell and SCell). The message generation and interpretation unit1121 transmits the control information to the UE and interprets theinformation carried in the received message. The message generation andinterpretation unit 1121 may be a MAC layer or RRC layer entity. Thecontext management unit 1131 manages the context of the UE, the cellsconfigured for the UE, and channel configuration resource. If it isdetected, by means of the transceiver 1101, that there is any problem inreceiving signals through the SCell or if the SCell requiring new uplinktransmission timing is activated by means of the context management unitfor the UE and the configuration resource, the MAC/RRC messagegeneration and interpretation unit 1121 configures the SCell identifierand uplink suspension indicator information and transmits thecorresponding message by means of the transceiver 1101.

FIG. 12 is a block diagram illustrating the UE according to anembodiment of the present disclosure. If the SCell activation message ora separate message is received form the eNB through a physicaltransceiver 1201 responsible for communication with the eNB, the MAC/RRClayer control message generation/interpretation unit 1221 interprets thecontrol information included in the message. The UE may turns on/off thetransmission of the control information/data buffered in the SRStransmission unit 1261 for the SCell and the MAC transmission buffer1211 using the scheduler 1241 by referencing the information included inthe SCell activation message and the separated message or the contextinformation of the corresponding SCell of the channelstructure/configuration information management unit 1231. Although theSRS and control information/data transmission for the SCell is off, ifthe eNB commands to perform the random access, the Random AccessPreamble transmission unit 1251 may transmits the Random Access Preambleunder the control of the scheduler 1241.

It will be understood that each block of the flowchart illustrationsand/or block diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks. These computer programinstructions may also be stored in a computer-readable memory that candirect a computer or other programmable data processing apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture includinginstruction means which implement the function/act specified in theflowchart and/or block diagram block or blocks. The computer programinstructions may also be loaded onto a computer or other programmabledata processing apparatus to cause a series of operational steps to beperformed on the computer or other programmable apparatus to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide steps forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Furthermore, the respective block diagrams may illustrate parts ofmodules, segments or codes including at least one or more executableinstructions for performing specific logic function(s). Moreover, itshould be noted that the functions of the blocks may be performed indifferent order in several modifications. For example, two successiveblocks may be performed substantially at the same time, or may beperformed in reverse order according to their functions.

The term “module” according to the embodiments of the invention, means,but is not limited to, a software or hardware component, such as a FieldProgrammable Gate Array (FPGA) or Application Specific IntegratedCircuit (ASIC), which performs certain tasks. A module mayadvantageously be configured to reside on the addressable storage mediumand configured to be executed on one or more processors. Thus, a modulemay include, by way of example, components, such as software components,object-oriented software components, class components and taskcomponents, processes, functions, attributes, procedures, subroutines,segments of program code, drivers, firmware, microcode, circuitry, data,databases, data structures, tables, arrays, and variables. Thefunctionality provided for in the components and modules may be combinedinto fewer components and modules or further separated into additionalcomponents and modules. In addition, the components and modules may beimplemented such that they execute one or more CPUs in a device or asecure multimedia card.

The foregoing disclosure has been set forth merely to illustrate theinvention and is not intended to be limiting. Since modifications of thedisclosed embodiments incorporating the spirit and substance of theinvention may occur to persons skilled in the art, the invention shouldbe construed to include everything within the scope of the appendedclaims and equivalents thereof.

Although exemplary embodiments of the present invention have beendescribed in detail hereinabove with specific terminology, this is forthe purpose of describing particular embodiments only and not intendedto be limiting of the invention. While particular embodiments of thepresent invention have been illustrated and described, it would beobvious to those skilled in the art that various other changes andmodifications can be made without departing from the spirit and scope ofthe invention.

The invention claimed is:
 1. A method performed by a user equipment (UE)in a wireless communication system, the method comprising: receiving,from a base station, a radio resource control (RRC) message includinginformation on a timing advance group (TAG) of at least one secondarycell; determining whether a timer associated with the TAG to which aserving cell belongs is running; and not performing any uplinktransmission on the serving cell except a random access preambletransmission in case that the timer associated with the TAG is notrunning.
 2. The method of claim 1, further comprising: in case that thetimer associated with the TAG is running, performing the uplinktransmission on the serving cell.
 3. The method of claim 1, wherein theTAG is a group of serving cells using a same timing advance value,wherein the RRC message includes information for adding the at least onesecondary cell, and wherein the information on the TAG includes anidentity of the TAG.
 4. The method of claim 2, wherein the performingthe uplink transmission comprises: receiving scheduling information forthe uplink transmission through a physical downlink control channel(PDCCH), and performing the uplink transmission on the serving cellbased on the scheduling information.
 5. A method performed by a basestation in a wireless communication system, the method comprising:transmitting, to a user equipment (UE), a radio resource control (RRC)message including information on a timing advance group (TAG) of atleast one secondary cell; and receiving, from the UE, an uplinktransmission on a serving cell in case that a timer associated with theTAG to which the serving cell belongs is running, wherein any uplinktransmission on the serving cell except a random access preambletransmission is not performed in case that the timer associated with theTAG is not running.
 6. The method of claim 5, wherein the TAG is a groupof serving cells using a same timing advance value, wherein the RRCmessage includes information for adding the at least one secondary cell,and wherein the information on the TAG includes an identity of the TAG.7. The method of claim 5, wherein the receiving the uplink transmissioncomprises: transmitting, to the UE, scheduling information for theuplink transmission through a physical downlink control channel (PDCCH),and receiving, from the UE, the uplink transmission on the serving cellbased on the scheduling information.
 8. A user equipment (UE) in awireless communication system, the UE comprising: a transceiver; and acontroller configured to: receive, from a base station via thetransceiver, a radio resource control (RRC) message includinginformation on a timing advance group (TAG) of at least one secondarycell, determine whether a timer associated with the TAG to which aserving cell belongs is running, and not perform any uplink transmissionon the serving cell in case that the timer associated with the TAG isnot running.
 9. The UE of claim 8, wherein the controller is configuredto perform the uplink transmission on the serving cell, in case that thetimer associated with the TAG is running.
 10. The UE of claim 8, whereinthe TAG is a group of serving cells using a same timing advance value,wherein the RRC message includes information for adding the at least onesecondary cell, and wherein the information on the TAG includes anidentity of the TAG.
 11. The UE of claim 9, wherein the controller isfurther configured to: receive, from the base station via thetransceiver, scheduling information for the uplink transmission througha physical downlink control channel (PDCCH), and perform the uplinktransmission on the serving cell based on the scheduling information.12. A base station in a wireless communication system, the base stationcomprising: a transceiver; and a controller configured to: transmit, toa user equipment (UE) via the transceiver, a radio resource control(RRC) message including information on a timing advance group (TAG), andreceive, from the UE via the transceiver, an uplink transmission on aserving cell in case that a timer associated with the TAG to which theserving cell belongs is running, wherein any uplink transmission on theserving cell except a random access preamble transmission is notperformed in case that the timer associated with the TAG is not running.13. The base station of claim 12, wherein the TAG is a group of servingcells using a same timing advance value, wherein the RRC messageincludes information for adding the at least one secondary cell, andwherein the information on the TAG includes an identity of the TAG. 14.The base station of claim 12, wherein the controller is furtherconfigured to: transmit, to the UE via the transceiver, schedulinginformation for the uplink transmission through a physical downlinkcontrol channel (PDCCH), and receive, from the UE via the transceiver,the uplink transmission on the serving cell based on the schedulinginformation.
 15. The method of claim 1, further comprising: receiving amedium access control (MAC) control information including informationfor activating the at least one secondary cell; receiving a PDCCH orderin case that the timer associated with the TAG is not running;performing, on a secondary cell associated with the TAG, the randomaccess preamble transmission based on the PDCCH order; receiving, on aprimary cell, a random access response including a timing advancecommand as a response to the random access preamble transmission; andapplying the timing advance command for the TAG.
 16. The method of claim5, further comprising: transmitting, to the UE, a medium access control(MAC) control information including information for activating the atleast one secondary cell; receiving, from the UE, a PDCCH order in casethat the timer associated with the TAG is not running; receiving, on asecondary cell associated with the TAG, the random access preambletransmission based on the PDCCH order; transmitting, on a primary cell,a random access response including a timing advance command as aresponse to the random access preamble transmission; and applying thetiming advance command for the TAG.
 17. The UE of claim 8, wherein thecontroller is further configured to: receive, via the transceiver, amedium access control (MAC) control information including informationfor activating the at least one secondary cell, receive, via thetransceiver, a PDCCH order in case that the timer associated with theTAG is not running, perform, on a secondary cell associated with theTAG, the random access preamble transmission based on the PDCCH order,receive, on a primary cell via the transceiver, a random access responseincluding a timing advance command as a response to the random accesspreamble, and apply the timing advance command for the TAG.
 18. The basestation of claim 12, wherein the controller is further configured to:transmit, to the UE via the transceiver, a medium access control (MAC)control information including information for activating the at leastone secondary cell, receive, from the UE via the transceiver, a PDCCHorder in case that the timer associated with the TAG is not running,receive, on a secondary cell associated with the TAG, the random accesspreamble transmission based on the PDCCH order, transmit, on a primarycell via the transceiver, a random access response including a timingadvance command as a response to the random access preambletransmission, and apply the timing advance command for the TAG.